Question

The minimum distance to hear a clear echo is (V is the velocity of sound)

• A. 2V/5
• B. 5V/2
• C. V/20
• D. 5V

Answer 1

The correct option is C V/20

Minimum frequency to the human ear is 20
$\therefore T=\frac{1}{F}$
$T=\frac{1}{20}$
$d=V\times t$
$d=V\times \frac{1}{20}$
$\therefore$ The minimum distance is$\frac{V}{20}$, where V is speed of the sound.